Serving Size, Calories, Daily Values, and Food Labels

Date: 05/26/2005 at 15:35:52
From: joe
Subject: how to determine the serving size and % DV
I'm trying to figure out the equations used for values that are
displayed on a food label. I can't figure how they determine the
serving size and the grams involved. For example:
serving size 1 cup (228g)
calories 250 %DV
Total Fat 12g 18%
Saturated Fat 3g 15%
I can't come up with an equation nor the possible variables that might
be used to determine these results.

Date: 05/27/2005 at 09:48:12
From: Doctor Wilko
Subject: Re: how to determine the serving size and % DV
Hi Joe,
Thanks for writing to Dr. Math!
Good question. I'd say you'd probably get more insight into food
labels and nutrition by going to the Internet and searching for some
good websites that discuss "nutrition" or "nutrition labels". One
good starting point might be the FDA's site:
http://www.fda.gov
As I saw your question come through, I was sitting here eating a bag
of Famous Amos Chocolate Chip Cookies and thought, "Perfect, let's try
it!"
The label looks as follows:
-----------------------------------------------
Serving Size 1 package, 1 serving per container
Calories 280, Calories from Fat 120
-----------------------------------------------
Total Fat 13g 20%DV
Sat Fat 4.5g 23%DV
Total Carbs 38g 13%DV
Fiber 1g 4%DV
Protein 3g --
------------------------------------------------
If you notice, the labels will usually say, "Percent Daily Values are
based on a 2,000-calorie diet." Then the legend below will be listed.
This legend is how you calculate the %DV:
------------------------------------------------
For a 2,000-Calorie Diet:
Total Fat should be less than 65g
Saturated Fat should be less than 20g
Total Carbs should be less than 300g
Dietary Fiber should be 25g
------------------------------------------------
Let's calculate the %DVs and see if we are close to the label.
The way we do this is just make a ratio of the amount of nutrient in
one serving size over the recommended daily amount (based on a 2000-
calorie diet).
Total Fat: 13g/65g = 0.20 = 20% DV
Sat Fat: 4.5g/20g = 0.225 = 22.5% DV (Label rounded to 23%)
Total Carbs: 38g/300g = 0.126.. = 12.7% DV (Label rounded to 13%)
Dietary Fiber: 1g/25g = 0.04 = 4% DV
Our calculations look good. Remember the %DVs are not recommended
intakes, but just reference points to help people gauge what their
overall dietary needs should be. Again, most labels calculate the
%DV from a 2,000-calorie diet. If you calculated these values from a
2,500-calorie diet, the %DV would be different from what's listed on
the package.
The only other math I can think of from the label is to see how they
calculate the "Total Calories" and the "Calories from Fat" at the top
of the label.
You do need some additional information that is not on the label to
do this. You need to know:
1g Fat = 9 calories
1g Protein = 4 calories
1g Carb = 4 calories
From here we can calculate the calories from fat. From the label, we
were given the following:
Total Fat 13g
Since 1g fat = 9 calories, then 13 * 9 = 117 calories from fat. The
label said 120 calories were from fat, so there may be some rounding
going on here, but we're still close.
Let's calculate the calories from protein and carbs to find the total
calories:
Total Carbs 38g
Since 1g Carb = 4 calories, then 38 * 4 = 152 calories from carbs.
Protein 3g
Since 1g Protein = 4 calories, then 3 * 4 = 12 calories from protein.
If we add these calories, we get:
117 calories from fat
152 calories from carbs
12 calories from protein
+ --------------------------
281 calories total (Label said 280 calories total)
This should give you some good insight into understanding nutrition
labels. Now the challenge is for you to take something from your
fridge and see if you can calculate the values like we've done above!
Does this help? Please write back if you have further questions.
- Doctor Wilko, The Math Forum
http://mathforum.org/dr.math/

Date: 06/06/2005 at 14:26:09
From: joe
Subject: Thank you (how to determine the serving size and % DV)
I want to thank you for this very helpful response. A million thanks!